Coupling elements include different types of couplers and power dividers in which input electromagnetic power is split to multiple different output ports. In, e.g., R. C. Frye et al., A 2 GHz Quadrature Hybrid Implemented in CMOS Technology, IEEE JSSC, vol. 38, no. 3, pp. 550-555, March 2003, the input signal is split into two signals that are 90 degrees apart in phase. The frequency at which these and other couplers operate has allowed them to be miniaturized and integrated on-chip, and there is a still growing interest in further reducing the size or footprint of couplers implemented in, e.g., wireless communication systems.
There is also a general tendency in chip design to reduce the supply voltage. A drawback with lower supply voltages is however that the noise immunity of the circuits may be impaired, which may reduce the signaling quality. Q. Shi et. al., A 54-69.3 GHz Dual-Band VCO with Differential Hybrid Coupler for Quadrature Generation, Solid-State Circuits Conference (A-SSCC), 2013 IEEE Asian, pp. 325,328, 11-13 November 2013, provides differential signaling by connecting two single ended quadrature hybrids. Such a duplicated quadrature hybrid however requires a relatively large area and may increase the footprint of the circuit.
There is hence a need for a coupler that has a relatively small footprint and that is less sensitive to noise, e.g. external noise and/or noise induced from the power supply and/or neighboring circuits.